The present invention relates to an autochanger type disc player suited to optical compact discs, for example.
Recently, in the field of audio equipment, digital audio disc playback systems utilizing pulse code modulation (referred as PCM hereinafter) technology to play back sound as faithfully as possible have been developed. Of these systems, playback systems employing optical compact discs have been especially popular.
Specifically, the optical compact disc used in the playback system consists of a disc which is made from a transparent resin and has a diameter of 12 cm and a thickness of 1.2 mm. The compact disc has a thin metal film deposited on at least one surface thereof, and pits or depressions are formed in the thin metal film, corresponding to digitized (pulse code-modulated) data so that logic 1 and 0 may produce different light reflectivities. When a signal is read out from the compact disc, the compact disc is rotated at a variable rotation frequency of 200 to 500 rpm so that an optical pickup incorporating a semiconductor laser or photoelectric transducing device tracks the information storage area of the compact disc with constant linear velocity while moving radially from the inner side toward the outer side.
The compact disc stores such a large quantity of information that it permits a stereophonic playback for about one hour even if only one side of the compact disc is used for information storage. It has been theoretically proved that the compact disc is much superior to the conventional analog phonograph record in both playback characteristics and recording density.
In view of the excellent characteristics of the compact disc, it has been suggested to use compact discs in an automatic multi-disc playback system for business use. In particular, this corresponds to a jukebox or an orchestra accompaniment playback apparatus (that is known as "karaoke" apparatus in Japan) which is put into practical use with analog phonograph records. It is possible to realize the automatic multi-disc playback system by means of an autochanger type disc player. Known autochanger type disc players of this kind are complex in structure and bulky, however, partially because they have been designed for use with analog phonograph records. Therefore, the conventional disc players present control problems. Further, the requirement of more certain operation limits the number of discs held within such a disc player. Another problem is the long time it takes to exchange one disc for another. Also, a pusher-type mechanism has been used to take a disc from storage to a playing position. The pusher mechanism passes through the stack of discs and requires the discs to be separated by an unnecessarily wide space to accommodate the bulk of the pusher mechanism.
For these reasons, if the conventional autochanger type disc player is applied to compact discs without changing the essential structure of the disc player, there arise numerous problems. Hence, the development of an autochanger type disc player suited for compact discs is a matter of urgency.
The same circumstances apply to video disc players and optical disc document file systems which are soon to be put into practical use.